The first line means that the document system multiplexer is used when
a document is read. This multiplexer makes sure that the correct reader
for a format is used. The second line instructs the multiplexer to try
to parse all documents with the XML reader first. (The xmlread plugin
parses an XML file faster than the tinyxml plugin, however, only the
latter one supports creation and modification of XML files - which usually
isn't needed for map files and alike.)

If You Parse Documents Manually

If you read CS documents manually somewhere in your app, you should
use the following snippet to obtain a document system object: